Crystal mounting



March 5, 1957 E. J. PURDUE CRYSTAL MOUNTING Filed May 18, 1954 K v n n um \l...

. IN V EN TOR. fDWfliD i Pumas lffdE/Yi/ United States Patent CRYSTAL MOUNTING Edward J. Purdue, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 18, 1954, Serial No. 430,587 8 Claims. (Cl. 310-94) The invention relates to piezoelectric crystal apparatus, and particularly to a device for mounting and holding piezoelectric crystals. The invention is an improvement over the device described and claimed by Bigler in his Patent No. 2,676,275, entitled Piezoelectric Crystal Apparatus, and issued April 20, 1954.

In apparatus requiring low frequency piezoelectric crystals, special consideration must be given to the mounting and holding of such crystals so that they can resist the effects of external vibration and shock. While this invention may apply to crystals having various cuts and frequencies, it is particularly applicable to AT-cut piezoelectric crystals which oscillate at relatively low frequencies such as 500 kilocycles and 1000 kilocycles.

An object of the invention is to provide an inexpensive device for mounting and holding piezoelectric crystals which (a) allows the crystal to be easily inserted and positioned in the device for optimum operation, (12) is simple in structure, (0) resists external vibration and shock, and ((2') allows crystals to be inserted and withdrawn numerous times without damage to the crystal or to any part of its mounting.

Briefly, the invention provides for mounting a crystal between two posts. The two posts are channeled on their facing surfaces, and are bent or curved toward each other at their free ends. Prongs are connected to the two posts and secured to an insulating material such as glass. The ends of the prongs remote from the posts are brought out of the insulating material and serve as terminal connections. When the crystal is in its mounting, it is held by its edges which fit into the channels on the two posts. The two posts hold the crystal firmly and securely by exerting pressure inward toward each other, and downward toward the insulating material in which the posts are held. A strip of soft, resilient, insulating material placed between the lower edge of the crystal and the insulating material cushions the crystal from the downward pressure of the two posts. An electrode on one face of the crystal extends to one edge of the crystal that is in contact with one of the posts, and an electrode on the other face of the crystal extends to an opposite edge of the crystal that is in contact with the other post, thus providing electrical connection to the faces of the crystal. If desired, the entire mounting may be placed in a hermetically sealed container. When crystals are mounted in accordance with this invention, they remain unharmed and perform satisfactorily even after being subjected to the standard ten-inch drop test.

The invention is explained in detail in the following description with reference to the accompanying drawing, in which the same reference numerals refer to corresponding parts throughout the figures.

Fig. 1 shows a view partly in section of a piezoelectric crystal mounted according to one embodiment of the invention;

Fig. 2 shows a sectional view of the crystal and mounting taken along the line 2--2 in Fig. 1;

Fig. 3 shows an enlarged portion of the sectional view of Fig. 2; and

Fig. 4 shows a piezoelectric crystal mounted according to another embodiment of the invention.

Fig. 1 shows a circular piezoelectric crystal disc or wafer 10 that is ground to the thickness necessary to give the desired frequency of oscillation. While a round shape is shown, other shapes may also be mounted. A circular metallic electrode coating 11 and a conducting strip 12 that extends to one edge of the crystal 10 are bonded on one face of the crystal 10, and a second circular metallic electrode coating 13 and a conducting strip 14 that extends to the opposite edge of the crystal 10 are bonded on the opposite face of the crystal 19. Gold is one of the materials which has been used for forming these electrodes and conducting strips, and this material may be applied to the crystal by chemical deposition, evaporation or firing.

Opposite edges of the crystal 16, particularly in the vicinity of the conducting strips 12 and 14, are painted with a conductive paste such as silver, and fired, to form the conducting strips 15 and 16. These strips 15 and 16 are bonded to the strips 12 and 14 respectively, and to the crystal 10 to provide a connection to the faces of the crystal 10.

In Fig. l, the mounting device comprises an oblong metallic base 20, around which are a groove or channel 21 and a flange 22. Though not necessary, this channel 21 and flange 22 are provided for holding a protective cover, not shown, over the crystal and mounting. The metallic base 20 contains an insulating base 23, formed of an insulating material such as glass, which holds the metallic prongs 25 and 26 respectively. These prongs 25 and 26 serve as external connections for the mounted crystal.

The two posts 30 and 31 may be fastened to the prongs 25 and 26 respectively by any convenient method, such as spot welding. These posts 30 and 31 are formed from some metal such as cold-rolled steel so that they have the necessary strength and resiliency to hold the crystal 10 firmly, and yet allow the crystal it) to be easily mounted. They may also be plated with some conducting material, such as silver or copper. Two V-shaped channels 32 and 33 run along the posts 36 and 31 respectively. While the preferred channel is V-shaped, other shapes will serve to hold the crystal, through they will not hold the crystal as well, or make as good an electrical contact with the crystal. The two posts 36 and 31 are positioned so that their respective channels 32 and 33 face toward each other. Near their free end, the two posts 30 and 31 are bent toward each other as shown in Fig. 1, so that they form as nearly tangential contacts as possible with the crystal 10 when it is inserted in its mounting.

When a crystal 10 is placed in the mounting, the two posts 30 and 31 are spread apart slightly to allow the crystal 10 to be placed between them. With the ciystal 10 in position, the two posts 30 and 31 are allowed to bend back toward each other, so that the channels 32 and 33 firmly hold and make contact with the crystal 10 at four points along its edges. The downward pressure on the crystal 10 is absorbed by a cushion made of soft, resilient, insulating material, such as Teflon. It is preferable that this cushion 4% be a rectangular strip that is notched at its ends, so that it will be held between the prongs 25 and 26 when the crystal it) is in its mounting. If desired, an indentation 41 may be stamped into the cushion 40 to remove any possibility of the cushion 40 shifting after the crystal 10 is mounted.

A clearer understanding of the crystal mounting may be obtained from Figs. 2 and 3. Fig. 2 is a sectional view of the crystal and its mounting taken along the line 2-2 in Fig. l, and Fig. 3 is an enlarged portion of the sectional view of Fig. 2. Fig. 2 shOWs the crystal 10 mounted and held at its edges by the posts 5t and '31 respectively, which engage the conducting strips 15 and 1e. Fig. 3 shows in detail how the edge of the crystal iiihaving the conducting strip 15 makes good electrical contact with the V-shaped channel 32 of the post 3d. The mounting'of the edge of the crystal 1% having the conducting strip 16 in the V- shaped channel 33 i similar to that of Fig. 3.

Fig. 4 shows another embodiment of this invention in which the crystal it is mounted between two posts 50 and 51 that are symmetrically curved inward toward each other to fit around the edges of the crystal 10. These posts Sil'and 51 also have V-shaped channels 52 and 53 respectively, and are identical to the posts 30 and 31 in all respects except that they are curved instead of bent at one point. While the posts 59 and 51 may be more difiicult to manufacture, they give better support to, and make better contact with, the crystal 10.

The crystal lid mounted as shown in Figs. 1 and 4 is firmly supported about its edges, by the posts, and by the cushion. Good electrical contact from the posts to the conducting strips 15 and 15 and to the electrodes 11 and 13 is assured (espite external vibration and shock. Added protection to ti e crystal may also be obtained by placing a protective cover over the crystal and its mounting and in the channel 21, and hermetically sealing the cover to the rim 22.

The invention claimed is:

l. A crystal mounting comprising a base having two posts each having longitudinal grooves along their facing surfaces, said posts being bent towards each other at their free ends, each of the bent portions being adapted to engage and exert pressure on a crystal mounted therebetween in a direction toward the other post, whereby said crystal is held at a plurality of points along the length of each of said posts.

2. A crystal mounting comprising an insulating, base, two posts mounted in said base, said posts having longitudinal channels along the entire length of their facing surfaces and being bent toward each other at their free ends, and a strip of cushioning material positioned between said posts near their point of entry into said insulating base, each of said posts and the bent portions being adapted to engage and exert pressure on a crystal mounted therebetween in a direction toward the other post, whereby said crystal is held at a plurality of spaced point along the length of each of said channels and supported by said cushioning material.

3. A crystal mounting comprising a metallic base, an insulating base contained by said metallic base, a pair of metallic prongs mounted in said insulating base and extending therethrough, metallic posts each having longitudinal channels along the entire length thereof and mounted on adjacent ends of said prongs so that said channels face each other, said posts being bent toward each other at their free ends, and a strip of cushioning and insulating material positioned between said prongs near their point of entry into said insulating base, each of said posts and the bent portions being adapted to engage and exert pressure on a crystal mounted therebetween in a diell) rection toward said base and toward the other post, whereby said crystal is held at a plurality'of spaced points along the length of each of said channels and supported by said cushioning material.

4. A crystal mounting as defined in claim 3 wherein said channels are V-shaped.

5. A crystal mounting as defined in claim 3 wherein said posts are bent at one point so as to tangentially engage the edge of said crystal.

6. A crystal mounting as defined in claim 3 wherein said posts are bent at a plurality of points so as to form a curve substantially conforming with the edge of said crystal.

7. In combination, a mounting for a crystal disc comprising an oblong metallic base, an insulating base contained by said metallic base, a pair of spaced metallic prongs mounted in said insulating base and extending therethrough, metallic posts mounted on adjacent ends of said prongs and on the same side of said insulating base facing each other, said posts having longitudinal V-shaped channels on their facing surfaces and each having a bend in its upper portion at a point intermediate their ends, each bent portion extending in the direction of the other post and arranged to contact and exert pressure on the peripheral edge of said crystal. disc, said points being substantially the same distance from said metallic base, a rectangular cushion of insulating material having notched ends and an indentation in one of its large faces andbeing positioned so that said notched ends are between and against said prongs at their point of entry into said insulating base, and a piezoelectric crystal disc mounted with its edges in said channels and in said indentation and held between said posts and against said cushion by the pressure exerted by said posts and said bent portions thereof.

8. in combination, a mounting for a crystal disc comprising an oblong metallic base, an insulating base contained by said metallic base, a pair of spaced metallic prongs mounted in said insulating base and extending therethrough, metallic posts mounted on adjacent ends of said prongs and on the same side of said insulating base facing each other, said posts having longitudinal ti-shaped channels on their facing surfaces and each being curved near their free ends, each of the curved portions extending in the direction of and symmetrically with the other curved portion and arranged to contact and exert pressure on the peripheral edge of said crystal disc, a rectangular cushion of insulating material having notched ends and an indentation in one of its large faces and being positioned so that said notched ends are between and against said prongs at their point of entry into said insulating base, and a piezoelectric crystal disc mounted with its edges in said channels and in said indentation and held between said posts and against said cushion by the pressure exerted by said posts and said curved portions thereof.

References Cited in the file of this patent UNITED STATES PATENTS 

